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CHAPTER 4: Results
Pellet-sinter at 850 °C for 12 hours in the air
Process conditions
The first step is to add LiOH into the end of life NCM (201810#2) Which Lix is 0.63. In this step, considering the evaporation of the LiOH, different amounts of LiOH (37% of Li, 40% of Li and 43% of Li) are added into the EOL NCM powder. Since the conditions of this group of experiments are pelleted mixture and sintering in air, three low amounts of LiOH have been chosen because the pelleted mixture has less surface which decreases the evaporation of the LiOH. Second, the mixture is pressed into small pellets in order to decrease the evaporation of the LiOH and increases the contact between LiOH particle and particle of the wasted NCM. Then the pelleted mixture is sintered at 850 °C for 12 hours in a tube furnace settled in air condition. After 12 hours and before the temperature decreases under 100 °C, the recycled NCM is moved into the glove box in order to avoid moisture effect.
Figure 19 shows the XRD patterns of wasted NCM powder (201810#2), EOL NCM powder with 37% of Li, 40% of Li, and 43% of Li which are pelleted and sintered at 850 °C for 12 hours in the air, and MTI commercial NCM (523) powder. The intens ity ratio of peak 102/ peak 006 is higher for sintered NCM powder and commercial powder compared with the EOL NCM. The small intensity ratio of peak 102/ peak 006 shows Lithium’s deficiency in the crystal structure. Therefore, there is no distinct differe nce between sintered NCM powder and commercial MTI powder. Figure 20 shows the particle size from the scanning electron microscope. The size of the particle which is at its end is in the range of 5 to 20 µm and the particle size of sintered NCM is between 5 to 25 µm. After sintering, the particle sizes increase a little bit. This crystal growth usually leads to better electrochemical performance under a high C rate. Also from image (a), the crack structure shows the deficiency of lithium in the EOL NCM Powder. This situation cannot be found in sintered NCM, which means that the cycled process recovers the broken structure of the wasted NCM.
Electrochemical performance.
Figure 21 shows the first circle EC performance profile and cycling performance of each recycled powder at C/5 rate cycling between 2.75 – 4.2V compared with the commercial MTI NCM 523 powder. For the EC performance of the MTI commercia l NCM 523 power, the first cycle charge capacity is 187.1 mAh/g and the first cycle discharge capacity is 158.5mAh/g. So the first cycle capacity irreversibility is 28.6mAh/g. After 2cycles, the charge and discharge capacities become stable (between 156-159 mAh/g). The first cycle capacity irreversibility of cycled NCM with 37% of Li is 35.6 mAh/g. The first cycle capacity irreversibility of cycled NCM with 40% of Li is 29.3 mAh/g. The first cycle capacity irreversibility of cycled NCM with 43% of Li is 25.3mAh/g. From the result, the first cycle capacity irreversibility of cycled NCM with 40% of Li, and cycled NCM with 43% of Li is lower than the commercial materia ls. In addition, the cycling capacities of cycled NCM with 43% of Li are similar to the commercial NCM. For cycled NCM with 37% of Li, the charge and discharge capacities are stable (between 143-145 mAh/g) after 2 cycles, which is lower than commercial NCM powder. For cycled NCM with 40% of Li, the charge and discharge cycles, the cycling performance of cycled NCM with 43% of Li is better than the commercial NCM. After 100 cycles, the capacity of commercial NCM decrease hastily. However, the capacity of cycled NCM with 43% of Li keeps around 150 mAh/g. It means cycled NCM with 43% of Li has better life cycles than commercial NCM.
Pellet-sinter at 850 °C for 12 hours in the oxygen
Process conditions
The first step is to add LiOH into the end of life NCM (201810#2) Which Lix is 0.63. In this step, considering the evaporation of the LiOH, different amounts of LiOH (37% of Li, 40% of Li, and 43% of Li) are added into the EOL NCM powder. Since the capacities of these three groups coin cells are deficient. Groups of 46% of Li and 49% of Li are tested. Therefore five different amounts of LiOH are added into the EOL NCM powder. Second, the mixture is pressed into small pellets in order to decrease the evaporation of the LiOH and increase the contact between LiOH particles and particles of the wasted NCM. Then the pelleted mixture is sintered at 850 °C for 12 hours in a tube furnace settled in oxygen condition. After 12 hours and before the temperature decreases under 100 °C, the recycled NCM is moved into the glove box in order to avoid moisture effect.
Partial size and structure analyze
Form Figure 22. Shows the XRD patterns of wasted NCM powder (201810#2), EOL NCM powder add 37% of Li, 40% of Li, 43% of Li which are pelleted and sintered at 850 °C for 12 hours in the oxygen, and MTI commercial NCM(523) powder. The intensity ratio of peak 102/ peak 006 is bigger for sintered NCM powder and commercial powder compared with the EOL NCM. The small intensity ratio of peak 102/ peak 006 shows Lithium’s deficiency in the crystal structure. Therefore, there is no distinct difference between sintered NCM powder and commercial MTI powder. Figure 23 shows the particle size from the scanning electron microscope. The particle size of the end of life is in the range of 5 to 20 µm and the particle size of sintered NCM is between 5 to 25 µm. After sintering, the particle sizes increase a little bit. This crystal growth usually leads to better electrochemical performance under a high C rate. Also from image (a), the crack structure shows the deficiency of Lithium in the EOL NCM Powder. This situation cannot be found in sintered NCM which means that the cycled process recovers the broken structure of the end of life NCM.
Electrochemical performance.
Figure 24 shows the first circle EC performance profile and cycling performance of each recycled powder at C/5 rate cycling between 2.75 – 4.2V compared with the commercial MTI NCM 523 powder. For the EC performance of the MTI commercia l
is 25 mAh/g. From the result, the first cycle capacity irreversibility of recycled NCM is lower than the commercial martial. However, the cycling capacities of recycled NCM is lower than commercial NCM. For add 37% of Li cycled NCM after 2 cycles, the charge and discharge capacities are stable (between 136-138 mAh/g) which is much lower than commercial NCM powder. For add 40% of Li cycled NCM after 2 cycles, the charge and discharge capacities are stable (between 138-141 mAh/g) which is much lower than commercial NCM powder. For adding 43% of Li cycled NCM after 2 cycles, the charge and discharge capacities are stable (between 138-141 mAh/g) which is much lower than commercial NCM powder. For adding 46% of Li cycled NCM after 2 cycles, the charge and discharge capacities are stable (between 147-149 mAh/g) which is also lower than commercial NCM powder. For adding 49% of Li cycled NCM after 2 cycles, the charge and discharge capacities are stable (between 148-150 mAh/g) which is little lower than commercial NCM powder the cycle performance will be compared after 150 cycles.
Powder-sinter at 850 °C for 12 hours in the air
Process conditions
The first step is to add LiOH into the end of life NCM (201810#2) Which Lix is 0.63. In this step, considering the evaporation of the LiOH, different amounts of LiOH (43% of Li, 46% of Li, and 49% of Li) are added into the EOL NCM powder because the powder will not be pelleted compared with pelleted group tests. Therefore three different amounts of LiOH are added into the EOL NCM powder. Second, the mixture is not pressed into small pellets at this time. Then the mixture is sintered at 850 °C for 12 hours in a furnace settled in air condition. After 12 hours and before the temperature decreases under 100 °C, the recycled NCM is moved into the glove box in order to avoid moisture effect.
Partial size and structure analyze
Form Figure 25, it shows the XRD patterns of wasted NCM powder (201810#2), EOL NCM powders add 43% of Li, and 46% of Li, and 46% of Li pelleted and sinter at 850 °C for 12 hours in oxygen, and MTI commercial NCM523 powder. The intens ity ratio of peak 102/ peak 006 is bigger for sintered NCM powder and commercial powder comparing with the EOL NCM. The small intensity ratio of peak 102/ peak 006 shows Lithium deficiency in the crystal structure. Therefore, there is no distinct differe nce between sintered NCM powder and commercial MTI powder. Figure 26 shows the particle size from the scanning electron microscope. The particle size of the end of life is in the range of 5 to 20 µm, and the particle size of sintered NCM is between 5 to 25 µm. After sintering, the particle sizes increase a little bit. This crystal growth usually leads to better electrochemical performance under a high C rate. Also, the crack structure, which shows the lithium deficiency in the EOL NCM Powder cannot be found in sintered NCM which means that the cycled process recover the broken structure of the end of life NCM.
Electrochemical performance.
Figure 27 shows the first circle EC performance profile and cycling performance of each recycled powder at C/5 rate cycling between 2.75 – 4.2V compared with the commercial MTI NCM 523 powder. For the EC performance of the MTI commercia l NCM 523 power, the first cycle charge capacity is 187.1 mAh/g, and the first cycle discharge capacity is 158.5mAh/g. So the first cycle capacity irreversibility is 28.6mAh/g. After 2cycles, the charge and discharge capacities become stable (between 156-159 mAh/g). The first cycle capacity irreversibility of adding 43% of Li cycled NCM is 46 mAh/g. The first cycle capacity irreversibility of adding 46% of Li cycled NCM is 41.4 mAh/g. The first cycle capacity irreversibility of adding 49% of Li cycled NCM is 42.9 mAh/g. From the result, the first cycle capacity irreversibility of recycled NCM is much larger than the commercial martial. And the cycling capacities of recycled NCM is also lower than commercial NCM. For adding 43% of Li cycled NCM after 2 cycles, the charge and discharge capacities are stable (between 107-112 mAh/g) which is much lower than commercial NCM powder. For adding 46% of Li cycled NCM after 2 cycles, the charge and discharge capacities are stable (between 121-124 mAh/g) which is also higher than adding 46% of Li cycled NCM but still much lower than commercial NCM materials. For adding 49% of Li cycled NCM after 2 cycles, the charge and discharge capacities are stable (between 121-123 mAh/g) which is also much lower than commercial NCM materials.
Powder-sinter at 850 °C for 12 hours in the oxygen
Process conditions
In this group of the test, the process is similar to the previous test. The only difference is that the mixture is not pelleted before sintering. The whole process is as shown below: the first step is to add LiOH into the end of life NCM (201810#2) Which Lix is 0.63. Since in the previous test, the EC performance results of adding 37% of Li and 40% of Li are very low. Moreover, comparing two test conditions, un-pelleted mixture should have more evaporation of the LiOH than the pelleted mixture. Adding 43% of Li becomes the start level. Therefore, three different amounts of LiOH are added into the EOL NCM powder (add 43% of Li, add 46% of Li and add 49% of Li). Second, the un-pelleted mixture is sintered at 850 °C for 12 hours in the tube furnace settled in oxygen condition. After 12 hours and before the temperature decreases under 100 °C, the recycled NCM is moved into the glove box to avoid moisture effect.
Partial size and structure analyze
Figure 28 shows the XRD patterns of end of life NCM powder (201810#2), EOL NCM powder adds 43% of Li, 46% of Li, and 49% of Li which are un-pelleted and sintered at 850 °C for 12 hours in oxygen, and MTI commercial NCM(523) powder. The intensity ratio of peak 102/ peak 006 is bigger for sintered NCM powder and commercial powder comparing with the EOL NCM. The small intensity ratio of peak 102/ peak 006 shows Lithium deficiency in the crystal structure. Therefore, there is no distinct difference between sintered NCM powder and commercial MTI powder. Form Figure 29, it shows the particle size from the scanning electron microscope. The particle size of the end of life is in the range of 5 to 20 µm and the particle size of sintered NCM is between 10 to 25 µm. After sintering, the particle sizes increase a little bit. This crystal growth usually leads to better electrochemical performance under a high C rate. Also from image (a), the crack structure shows the lithium’s deficiency in the EOL NCM Powder. This situation cannot be found in sintered NCM which means that the cycled process recover the broken structure of wasted NCM.
Electrochemical performance.
cycles cycling performance of add 49% of Li cycled NCM is better than Commercia l NCM. For the other two recycled NCM, adding 43% of Li cycled NCM after 2 cycles, the charge and discharge capacities are stable (between 128-131 mAh/g) which is much lower than commercial NCM powder. For adding 46% of Li cycled NCM after 2 cycles, the charge and discharge capacities are stable (between 142-144 mAh/g) which is also lower than commercial NCM material.
Conclusion
From the results of four groups of tests, all the partial sizes and structures become better compared with the waste NCM523 after lithium adding and sintering process. The EC performance shows that the recycled NCM has a better performance, which is close to commercial NCM under two conditions. The first condition is pellet-sinter at 850 °C for 12 hours in oxygen. And the second condition is the pellet-sinter at 850 °C for 12 hours in the air. For the first condition, after pelleted mixture (49% of Li added) was burned at 850 °C for 12 hours in oxygen, the charge and discharge capacities are stable (between 148-150 mAh/g), which is close to theoretical capacity and capacity of commercial MTI NCM 523 powder. The cycling performance will be checked in the future. For the second condition, after the pelleting mixture (43% of Li added) was burned at 850 °C for 12 hours in the air, the charge and discharge capacities are stable (between 151-155 mAh/g), which is similar to the commercial NCM powder. In addition, we can find that after 100 cycles, the cycling performance of recycled NCM with 43% of Li is better than the commercial NCM. The capacity of commercial NCM decrease hastily. However, the capacity of recycled NCM with 43% of Li keeps around 150 mAh/g after 100 cycles. It means that recycled NCM with 43% of Li has better life cycles than the commercial NCM. It can also be concluded sintered products with deficiencies of lithium have lower capacity. Powder-sintering products have a lower capacity than pellet sintering products with small-scale sintering because of higher lithium evaporation. Air-sintering products have a higher capacity than O2-sintering products, which means that the atmosphere does not improve the EC performance in small – scale sintering. In the future, I will try to recycle on large scale sintering under different conditions and try to recycle different types of NCM.
TABLE OF CONTENTS
CHAPTER 1: Introduction
1.1 History of lithiumion battery
1.2 Structure of lithiumion batteries
1.3 Demand for recycling
1.4 Recycling methods
1.5 Methods to improve the electrochemical performance of lithium nickel cobalt manganese oxide (NCM) cathode
CHAPTER 2: Experimental Methodology
CHAPTER 3: Commercial material
CHAPTER 4: Results
4.1 Pellet sinter at 850 °C for 12 hours in the air
4.2 Pellet sinter at 850 °C for 12 hours in the oxygen
4.3 Powder sinter at 850 °C for 12 hours in the air
4.4 Powder–sinter at 850 °C for 12 hours in the oxygensinter at 850 °C for 12 hours in the oxygen
CHAPTER 5: ConclusionConclusion
References
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